The invention relates to the field of optical detection and the formation of extensive object images. It more specifically relates to an optical system for observation in real time which utilizes, for the purpose of amplifying the signal to be detected, the possibility provided by certain media of generating in real time a complex wave front.
The invention aims to improve the detection and imaging of extensive and/or remote objects.
Known observation and detection devices generally comprise a light source making it possible to illuminate the object to be detected via an illumination device transmitting energy radiated by the source onto the object. The illuminated object reflects at least part of the radiation received to a detection device comprising, inter alia, a collecting optical system which serves to form an image of the illuminated object on a detector, photosensitive support, photodetector, mosaic of photodetectors, vidicon, etc.
It is known to increase the sensitivity of the system by concentrating the illuminating beam onto a point of the object and by means of an X-Y deviator making the said beam undergo scanning in such a way that it successively illuminates all the points of the object. In this case, it is advantageous to receive the optical signal to be detected on a photodetector coupled to a television-type display, whose scanning is synchronous with the X-Y deviator. Thus, a bidimensional image of the object is obtained on the display.
For the purpose of detecting remote objects, it is advantageous to use infrared radiation, which is absorbed less by the ambient medium than visible radiation. The disadvantage is that in this wavelength range the detectors are not very sensitive.
The real time observation system according to the invention comprise the main elements of a conventional detection system. However, in order to significantly amplify the optical signal to be detected, a device able to generate in real time a complex wave front, isomorphic of the wave front of the optical signal to be detected and which serves to strengthen it is inserted into the same. By traversing said device and in conjunction with a pumping wave, the wave to be detected coming from the object records a diffraction grating therein. Following a recording time, the device diffracts a replica of the object wave, which contains part of the energy of the pumping wave and which is phase-matched with the object wave for the complete wave front. This replica can have a much greater intensity than the wave to be detected and is used in the system according to the invention for strengthening it on the detector, particularly by using a heterodyne detection.